The V8 Owners Forum -

I’ve been having rough running at idle and smells quite rich, it has power through the range it just misfires at idle and plugs are black wet and oily. Done a vacuum leak smoke test that the only place it leaks is from under the distributor cap (not sure if that’s normal?) vacuum pressure test is 11hg so on the low side. Compression test lowest 155psi and highest 170psi. I’ve checked the sensors with a dmm and in roverguage and they all checked out. Injectors are refurbished and checked the fuel pressure 36psi when disconnected fpr and 27 when connected with engine running, also holds pressure when not running. It’s had a new ignition system with new distributor leads and plugs. I’m confused why it’s leaking from the distributor? It’s a 3.5 with a 3.9 plenum and 14cux ecu

What cam are you running? One with high overlap will result in lower than expected compression test values (although a 15PSI spread seems a little high) and higher than expected manifold pressure (lower vacuum) at idle. I don't understand hg but 11 seems like that will be about 62.75kPa.
Mine runs about 155PSI compression and 55kPa manifold pressure at idle.
Unfortunately I don't know what cam mine has, was in the engine when I bought it, may have to measure the lift/duration at some point.